1. Field of the Invention
The present invention relates to a Cathode Ray Tube (hereinafter, CRT) and particularly, to a frame of a CRT, capable of preventing tension lowering and creep phenomena caused by heat processing and howling phenomenon of the cathode ray tube.
2. Description of the Background Art
Generally, a flat screen color CRT, as shown in FIG. 1, is composed of a front glass which is called as a panel 10 and a rear glass which is called as a funnel 20 and they are combined to each other, being enclosed with a high-degree vacuum.
Inside the CRT, a fluorescent layer 40 which functions as a predetermined luminescent material is formed on an inner surface of the panel 10. An electron gun 130 for scanning an electron beam for emitting the fluorescent surface 40. A shadow mask 70 for sorting colors so that the electron beam 60 generated in the electron gun 130 can be landed to a predetermined portion of the fluorescent layer 40. A main frame 30 and sub frame 35 fix and support the shadow mask 70 and a spring 80 combines the assembly of the above frames into the panel 10. An inner shield 90 which is combined with a side surface of the main frame 30 in a spanned shape from the side of the panel 10 to the side of the funnel 20, is positioned on one side surface of the main frame 30, so that the CRT is rarely influenced by a terrestrial magnetism, in operating the CRT.
Also, the flat screen CRT is provided with a reinforcing band 110 installed in the outer circumferential portion of the panel 10 and funnel 20, and accordingly, the flat screen CRT is constructed to have a sufficient resistance against air pressure and exterior impact.
On the other hand, the operation of the CRT shown in FIG. 1 will be described as follows.
First, the electron beam 6 is landed to the fluorescent layer 40 formed on the inner surface of the panel 10 in the electron beam landed to a neck portion of the funnel 20 by positive voltage applied to the CRT. At this time, the electron beam 60 is deflected to the upper and lower directions and left and right directions by the deflection yoke 50 before it reaches the fluorescent layer 40, thus to form a screen.
In addition, a magnet 100 having 2, 4 and 6 poles, for correcting the circle of the process so that the electron beam 60 can exactly land to a predetermined fluorescent material prevents degradation of color purity.
Since such CRT is composed under the condition of high-degree vacuum, a crack can be easily occurred by exterior impact. To prevent the crack, the flat screen CRT is provided with a reinforcing band formed on the circumferential surface of the skirt portion of the funnel 20, and accordingly, the flat screen CRT is constructed to have a sufficient impact resistance by dispersing stress formed in the CRT under the condition of a high-degree vacuum.
In a tension type CRT structure as in FIG. 1, to apply a tension to the shadow mask 70, a frame which supports the shadow mask 70 is compressed, a shadow mask is welded on the compressed frame and the compression added to the frame is stopped so that the tension is applied to the shadow mask 70.
FIG. 2 is a view showing the status that the frame for supporting the shadow mask is combined with the panel.
As shown in FIG. 2, a shadow mask 70 to which a tension is applied, is welded to the end of the main frame 30 and the frame 30 which applies a tension to the shadow mask 70 is combined with the panel 10, connected with a spring 80 and a stud pin 120 inside the panel 10.
Hereinafter, the composition that the shadow mask 70 is combined with the frame 30 will be described in detail.
Conventionally, a frame before being welded is compressed with a predetermined load and welded with the shadow mask 70. Then, a preferred curvature is embodied in the shadow mask by removing a compression load added to the frame and a tension is applied to the upper and lower directions (direction of the short-side line) at the same time. Accordingly, the natural frequency of the shadow mask is increased to prevent the howling phenomenon that a screen vibrates.
However, as the length of the screen is enlarged, the length of the short-side line (vertical direction) is increased and accordingly, the length of the short-side line (vertical direction) of the shadow mask capable of vibrating is lengthened.
Generally, since a natural frequency of a substance is inversely proportional to the length, as the length of the short-side line (vertical direction) of the shadow mask, the natural frequency of the shadow mask attached to the frame decreases.
Therefore, in the combination between the frame and shadow mask 70, the vibration which can be occurred in the shadow mask 70 must be considered due to an additional vibration which can be occurred by the exterior circumstance or in operating the frame and shadow mask 70.
Also, the tension applied to the upper and lower directions of the shadow mask 70 is related to the thickness of the shadow mask 70, heights of the main frame 30 and sub frame 35, curvature to the Z direction of the sub frame 35 and the like and the tension is also related to the ratio between the height of the whole frame and the height of the sub frame, compression load and material characteristic of the frame.
Hereinafter, among the above factors, relationship between the height of the sub frame 35 and the height of the whole frame, and the corresponding problems which is accompanied with the relationship will be described in detail.
First, in case the height of the sub frame 35 is composed smaller than that of the whole frame, that is, in case the curvature of the sub frame 35 is composed large, the suame 35 is composed large, the suth a larger compression load than in case the curvature is gentle, to apply a predetermined tension to the shadow mask 70.
However, since the capacity of the compression motor must be increased to add a larger compression load, the cost is increased.
In addition, the tension applied to the shadow mask 70 is determined according to the degree of the compression of the sub frame 35. The compression amount of the sub frame 35 can be known with the deflection length in the Z direction, which affects the tension applied to the shadow mask 70 as shown in FIG. 3B.
Also, in case the height of the sub frame 35 is composed smaller than that of the whole frame, the sub frame 35 must have a sufficient yield strength that it can stand the deflection force, since a larger stress is applied to the sub frame 35 to deflect the whole frame to the Z direction in FIG. 3b with the height as before.
However, since there is a limit with just the yield strength that the material itself has to have a sufficient yield strength, the material characteristic must be improved through the processing method such as additional heat processing of the frame member and the like and accordingly, the cost of the frame member itself is increased.
On the other hand, in case the height of the sub frame 35 is composed larger than that of the whole frame, that is, in case the curvature of the sub frame 35 is composed smaller, a preferred tension can be applied to the shadow mask 70 with a smaller compression load. Namely, as the curvature of the sub frame 35 is smaller, the sub frame can be compressed more easily.
However, in the composition of the sub frame having a larger height than the whole frame, the exterior portion of the sub frame 35, a round portion where the curvature is formed and a part can be protruded to the lower side of the skirt portion 11 of the panel 10.
In the above case, the panel 10 and the frames 30 and 35 must be moved under the condition that they are combined to each other in the manufacturing process of the CRT. In case the sub frame is protruded to the lower side of the skirt portion 11 of the panel 10, foreign material can be inserted to the shadow mask more in moving the panel and frames and the inflow of the foreign material causes a black point effect that the black dots are shown on a screen under the white condition after the CRT is manufactured, thus to degrade the screen characteristic.
Moreover, it is desirable that the band where the natural frequency of the shadow mask 70 is far from the band where the natural frequency of the frame is embodied since the shadow mask is vibrated by vibration of the speaker which is mounted in the product itself where the CRT is installed due to the resonance occurred between the frame and shadow mask in case the distance between the characteristics of the shadow mask 70 and the whole frames 30 and 35 is shortened.
In addition, the vibration of the shadow mask 70 affects the howling phenomenon caused by the vibration of the screen.
To solve the above problem, if the minimum tension amount applied to the shadow mask 70 is increased, the resonance can be easily avoided by becoming parted from the natural frequency of the frame. However, as described above, since the sub frame must have a sufficient yield strength to stand deflection in the Z direction in FIG. 3B, the cost is increased, according to the material characteristic.
Also, in the process of manufacturing the CRT, it includes a frit processing for attaching the funnel 20 to the rear surface of the panel 10 and heat processing for applying vacuum into the tube performed at 350 to 480xc2x0 C.
When the high temperature heat processing is performed under the condition that the tension is excessively applied to the corner portion of the shadow mask 70, the creep phenomenon which is not occurred at room temperature is occurred, thus to generate a wrinkle at the corner portion of the shadow mask 70.
Also, if the tension applied to the corner portion of the shadow mask exceeds a predetermined value, a wave wrinkle generated by buckling of the shaft of the sub frame 35. If the plastic deflection of the wrinkle is processed, the wave wrinkle of the shadow mask is remained.
To solve the above problem, the condition that the wrinkle is not generated has been obtained by experiments utilizing the method for adjusting the compression amount by changing the curvature of a clamping plate for clamping the shadow mask 70 or applying compression to the frame with the clamp plate.
However, in the method for compressing the frame, there was a problem that a sufficient amount of tension can not be applied to the both welding end portions of the shadow mask 70 and the main frame 30 and the wrinkle is occurred again because of the actual size of the components or subtle irregular composition of the device.
In addition, recently, as the screen of the CRT becomes flatter, the shape of the shadow mask 70 also becomes a flat shape. Accordingly, as the amount of the tension generated at the corner portion among the welding portions of the shadow mask 70 and frame 30 decreases, partial wrinkle is increasingly generated.
In case the partial wrinkle is occurred at the shadow mask 70, the fluorescent material can not be exposed with a uniform pitch width and the quality of the image is degraded.
Also, if the wrinkle is generated at the attached both end portions of the shadow mask 70 and frame 30, on the contrary, a sufficient amount of tension can not be applied to the corner portion of the shadow mask 70. Accordingly, the shadow mask 70 is vibrated at a lower frequency band and the vibration generated once can not easily attenuated.
Therefore, because of the above problem, the relative positions corresponding to the position of the fluorescent surface 40 inside the shadow mask 70 and panel 10 is changed and there can occur problems such as color impurity of the displayed image and the like.
Therefore, an object of the present invention is to provide a Cathode Ray Tube, capable of preventing the creep phenomenon which causes lowering of the tension after the heat processing and wrinkle to the corner portion of the shadow mask and preventing vibration of the shadow mask of the CRT considering instrumental formality with the panel, by setting an extent of the deflection length before compressing and after compressing of the frame, for applying an appropriate distribution of the tension to the shadow mask.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a CRT, including a panel in which a fluorescent surface is installed; a funnel which is fused and attached to the rear side of the panel using frit glass; a shadow mask having an electron beam through hole combined with the inner side surface of the panel to sort the color of the electron beam; and a mask assembly which is composed of a main frame for supporting the shadow mask and a sub frame for supporting the main frame. In addition, the following equation 0.40xe2x89xa6Ls/Lbxe2x89xa60.55 is satisfied when the minimum distance between the flat surface extended from the upper surface of the main frame and the flat surface extended from the lower surface of the sub frame in case a mask is removed from the mask assembly is Lb and the height of the sub frame is Ls.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a CRT, including a panel in which a fluorescent surface is installed; a funnel which is fused and attached to the rear side of the panel using frit glass; a shadow mask having an electron beam through hole combined with the inner side surface of the panel to sort the color of the electron beam; and a mask assembly which is composed of a main frame for supporting the shadow mask and a sub frame for supporting the main frame. In addition, the following equation 0.45xe2x89xa6(Lsxe2x88x92Lm)/Lbxe2x89xa60.59 is satisfied when the minimum distance between the flat surface extended from the upper surface of the main frame and the flat surface extended from the lower surface of the sub frame in case a mask is removed from the mask assembly is Lb and the height of the main frame is Lm.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.